PASCO ES-9078A User manual

Instruction Manual
012-12856A
Basic Electrometer
ES-9078A
800-772-8700 www.pasco.com
*012-12856*
®
Meter
display
Digits
display
Signal
Output
port
Voltage
range
indicators
Voltage
range
selector
push
button ON-OFFpush
button Ground port
Signal
Input
port
Access to
battery
compartment
ZERO
button
Included Items Included Items
Basic Electrometer Banana Plug Patch Cord*
BNC to Alligator Clip Cable* Alligator Clip*
Grounding Cable* AA-Cell Alkaline Battery (4) (not shown)
Interface Cable* (*shown on page 2)

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Basic Electrometer ES-9078A
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Other Equipment
Other PASCO equipment is recommended for use with the Basic Electrometer.
*See the PASCO catalog or the web site at www.pasco.com for more information
Introduction
The Model ES-9078A is a voltmeter used for direct measurements of voltage and indirect measurements of current and charge.
Because of its high (“infinite”) impedance of 1014 ohms, it is especially suited for measuring charge in electrostatic experiments. It
has a sensitivity nearly one thousand times that of a standard goldleaf electroscope, a center-zero meter display that directly indi-
cates charge polarity, and a digits display. The Basic Electrometer measures charges as low as 10-11 coulombs. The electrometer
can also output a signal (±10 V) to a PASCO interface.
With these features, you’ll find that your electrostatics demonstrations and labs are easier to perform and, with quantitative data,
are more informative. The electrometer is powered by four AA-alkaline batteries (included) which can be easily replaced by open-
ing the back casing.of the electrometer.
.
The Basic Electrometer includes four cables and a spare alligator clip.
The Banana Plug Patch Cord connects to the Ground port on the Basic Electrometer. The Signal Input Cable connects to the BNC
jack at the Signal Input Port. The Interface Cable connects between the Signal Output port of the Electrometer and a PASCO inter-
face. (NOTE: A PASPORT Analog Adapter PS-2158 is required to connect the cable to a PASPORT interface.) The Grounding
Cable has a one gigaohm resistor and is intended for use with the ES-9079 Basic Variable Capacitor.
Recommended Equipment* Recommended Equipment*
Faraday Ice Pail (ES-9042A) Basic Variable Capacitor (ES-9079)
Charge Producers and Proof Plane (ES-9057C) PASCO Interface and Data Acquisition Software
NOTE: When replacing batteries, do not touch any of the components or wires in the
integrated circuit panel; the components and wires are all static sensitive.
Signal Input Cable
(BNC-to-alligator clip)
Interface Cable
(mini-DIN to 8 pin DIN plug)
Grounding Cable
(insulated spade lug connectors)
Banana Plug
Patch Cord
Alligator clip
One gigaohm resistor
BNC plug
Figure 1: Cables and clip

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ES-9078A 012-12856A Operation
3
Operation
The controls on the front panel of the electrometer are explained in Figure 1. Whether you’re using the electrometer to measure
voltage, current, or charge, the following procedure should be followed each time you turn on the electrometer.
More information on making accurate measurements is provided in the sections that follow.
Setup
1. Connect the BNC plug of the signal input
cable (test lead) to the BNC jack on the side of
the electrometer. Line up the pegs on the BNC
jack with the slots on the BNC plug. Push the
plug onto the jack and turn the plug clockwise
one-quarter turn until it is secure.
2. Use the banana plug patch cord to connect the
ground port of the electrometer to an earth
ground.
3. Press the ON-OFF push buttonto turn the elec-
trometer on. The digits display, the meter dis-
play, and one of the voltage range indicators
will light up.
4. Press the ZERO button to zero the electrome-
ter. The light emitting diode (LED) of the
meter display will align with the “0” mark and
the digits display will show “0.0”.
You’re now ready to use the electrometer to mea-
sure charge, current or voltage.
5. Press the voltage range selector push button to
select the desired voltage range (3, 10, 30, or
100).
The range setting refers to the voltage input
required to produce a full-scale meter deflection
For example, a setting of 30 means that a full scale meter deflection indicates a voltage of 30 volts.
Warning:
1. Never use the electrometer for measuring potentials more than 100 volts.
2. Never connect the electrometer to an electrostatics generator, such as a Van de Graff generator
or a Wimhurst machine.
3. Avoid touching the input leads until you have grounded yourself to an earth ground. A person
walking across a rug on a cool dry day can easily acquire a potential of several thousand volts.
push to turn
ON and OFF
push to select
voltage range
connect
interface
cable here
connect signal
input cable here
connect to
earth ground
ZERO button
push to ground and
remove excess
charges
meter display
digits display
Figure 2: Electrometer Top Panel
(BNC jack)

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Basic Electrometer ES-9078A
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Measuring Voltage
The electrometer can be thought of as an infinite impedance voltmeter. To show that the electrometer is like a voltmeter, connect
the signal input cable leads to the battery, set the range (3, 10, 30, or 100 volts full scale), and read the voltage on the meter.
Measuring Charge
Induction Charges
Under most conditions, the best way to mea-
sure charge is by induction. Use a proof plane
and a Faraday ice pail, such as those included
with PASCO’s Electrostatics System
(ES-9080), and shown in Figure 3..
The proof plane is simply a small conductive
disk mounted on an insulating handle. To
sample the charge distribution on a charged
object, simply touch it with the proof plane,
then place the proof plane inside the inner cyl-
inder of the ice pail, without touching the cyl-
inder. A charge of equal magnitude and sign is
induced on the surface of the ice pail and can
be read by the electrometer.
By always using the proof plane and the ice
pail, the capacitance will be the same for all
your measurements, and the charge on the
proof plane will always be proportional to the
voltage reading of the electrometer.
Contact Charges
Charges can also be measured by contact. If you touch the inner cylinder of the ice pail with a charged object, for example a
charged proof plane, the electrometer reading will generally remain relatively unchanged. This is because the total capacitance is
only negligibly affected by the proof plane. This may not always be the case, however.
Any charge measurement with the electrometer is indirect, based on the knowledge that the amount of charge on an object is pro-
portional to the potential difference. The readings of the electrometer will always be of volts, not of coulombs. The polarity of the
voltage, however, directly shows the type of charge being sampled. If you need quantitative rather than qualitative charge measure-
ment, values for the charge can be computed according to the relationship Q = CV, where Vis the voltage across a known capacitor
of capacitance C.
Important Points for General Operations:
• Always press the ZERO button between measurements to discharge all excess charge from the
electrometer. Shorting the test leads together is insufficient. There may still be stray charges
within the electrometer circuitry.
• For good results, it is essential that the electrometer be connected to an earth ground (a water
pipe or the ground wire from a 120 VAC socket). Only an earth ground provides a sufficient
drain for excess charges that may build up during an experiment.
• It is also helpful if the experimenter is grounded. Just touch one hand to a good earth ground
just before, or during measurements.
Basic Electrometer
SignalInput
cable
black
clip red
clip
proof
plane
ice
pail shield
Figure 3: Electrometer with Faraday Ice
Faraday Ice Pail

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ES-9078A 012-12856A Measuring Current
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The electrometer can be thought of as an infinite impedance voltmeter in parallel
with a capacitor, CE, as shown in Figure 4. CErepresents the internal capacitance
of the electrometer, plus the capacitance of the leads and the capacitance of the
Ice Pail, if being used.
When a charged object is placed across the electrometer leads (or in the ice pail),
a voltage Vdisplays on the meter. If the value CEis known, the value of the
charge can be calculated as Q = CEV.
The capacitance of the electrometer alone is around 27 picofarads
(pF). However, if the sampled object adds significant capacitance,
the situation becomes as shown in Figure 5.
To accurately calculate the amount of charge, total capacitance CE
+ Cext must be determined. In any case, for quantitative measure-
ments of charge, you need to have an accurate value for CE(Cext
>>CE), unless you are certain that the object you are measuring has
a high enough capacitance to disregard CE. (This is not true, for
example, when using the ES-9079 Basic Variable Capacitor.)
The following process shows you how to measure an experimental value of the capacitance of the electrometer, any cables con-
nected to it, and the ice pail.
Measuring the Capacitance of the Electrometer and Connectors
For all experiments, the electrometer can be thought of as a voltmeter connected in parallel with a capacitor, as shown in Figure 3.
The capacitor CErepresents the internal capacitance of the electrometer, plus the capacitance of the leads and the ice pail. Use this
procedure to measure a precise value of the capacitance provided by the electrometer and all instruments connected to it. If you are
interested in qualitative, rather than quantitative experiments, this procedure is not necessary.
When a known capacitor C, is charged by a known voltage V, the charge in it is given by Q = CV. If the known charged capacitor is
connected across the leads of the electrometer, it is connected in parallel with the internal capacitance of the electrometer, CE. The
total capacitance becomes C + CE. The known capacitor discharges across the electrometer and a voltage, VE, is read.
Since the total charge in the system is still just the charge of the known capacitor, we know that CV = (C + CE) VE.
1. Obtain a low leakage capacitor (polypropylene, or air dielectric) of known value C, around 30 pF.
2. Charge the capacitor with a known voltage V, not higher than 100V (the limit of the electrometer).
3. Remove the charged capacitor from the power supply used to charge it, being careful not to ground it in any way, so as not to
remove the charge.
4. Connect the charged capacitor across the electrometer input leads. (Or across the pail and shield of the ice pail, if you want to
include its capacitance value). Note the voltage VE indicated by the electrometer.
5. Calculate the total capacitance:
Measuring Current
The electrometer can be used for indirect current measurements.
Connect the electrometer leads across a known resistance in the circuit and measure the voltage. Use Ohm’s Law (V = IR) to deter-
mine the current. Due to the electrometer’s exceedingly high input impedance, the effect of the electrometer in the circuit will be
Voltmeter
CE
Fig. 4: Ideal Schematic of the Electrometer
Voltmeter
CECext
Capacitance of
object connected
to the
electrometer
Fig. 5: Change in capacitance due to a charged object
CECV V
E
–
VE
-------------------------
=

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Basic Electrometer ES-9078A
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negligible in most circuits. However, the voltage drop across the resistor must be within the voltage range of the electrometer (100
V maximum).
If it is not convenient to hook the electrometer across a known resistance in the circuit, a precision resistor can be connected
between the input leads of the electrometer. The circuit can be broken, as for connection to a standard ammeter, and connected in
series with the precision resistor.
Again, measure the voltage across this resistor and calculate the current. (The problem with this technique is that the resistance
must be high enough to measure a voltage drop, but low enough so it doesn’t significantly affect the current through the circuit).
Electrometer with Interface
The signal output connector on the ES-9078A Electrometer provides an output signal for a PASCO interface. The interface cable
included with the electrometer connects directly to an analog channel on a ScienceWorkshop interface, and connects to a
PASPORT interface through a PS-2158 Analog Adapter. This enables the output signal from the electrometer to be recorded, dis-
played, and analyzed by the data acquisition software.
It is important to remember that the signal output on the ES-9078A has a fixed scale of ±10 volts. Changing the range switch on the
electrometer has no effect on this scaling. By choosing the Electrometer icon in DataStudio™ (data acquisition software), displays
are shown correctly scaled.
Because of limited resolution on this output, it may be useful to apply a gain within the data acquisition software to measure volt-
ages of less than 10 volts.
Experiment Setup: PASPORT
• Connect the mini-DIN plug of the interface cable to the Signal Output port on the electrometer. Connect the 8-pin DIN plug of
the interface cable to the PS-2158 Analog Adapter. Connect the Analog Adapter to a PASPORT Interface.
1. Start DataStudio. If the PASportal window opens, select “Launch DataStudio”. If the Welcome to DataStudio screen appears,
select “Create Experiment”. Otherwise, select “New Activity” from the File menu.
2. Select “Electrometer (Basic)” from the
list of sensors and click OK.
3. In the Displays list, click the Meter icon.
A Meter display of Voltage opens.
Experiment Setup: ScienceWorkshop
• Connect the mini-DIN plug of the interface cable
to the Signal Output port on the electrometer.
Connect the 8-pin DIN plug of the interface cable
to Analog Channel A of the ScienceWorkshop
Interface.
1. Start DataStudio. If the Welcome to DataStudio
screen appears, select “Create Experiment”. Oth-
erwise, select “New Activity” from the File menu.
2. In the Experiment Setup window, click the Ana-
log Channel A on the icon of the ScienceWorkshop interface.
Click Analog Channel A
Figure 6: Experiment Setup

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ES-9078A 012-12856A Specifications
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3. Select “Electrometer (Basic)” from the list of sensors and click OK.
4. In the Displays list, click the Meter icon. A Meter display of Voltage opens.
Data Recording
Note: Data recording is easier if one person handles the Electrometer and the other equipment and another person handles the com-
puter or data logger.
1. Prepare the Electrometer and equipment. Click “Start” to begin data recording.
2. Rub the two Charge Producers together. Lower the disk of one of the Charge Producers into the Faraday Ice Pail. Watch the
Meter display of voltage. Remove the first Charge Producer and put the second Charge Producer into the Faraday Ice Pail.
3. Click “Stop” to end data recording.
4. From the Displays list, click the Graph icon to view a plot of the voltage versus time that was recorded by the Electrometer.
Specifications
Item Value
Voltage input ranges 3, 10, 30, 100 volts full scale
Input resistance approximately 1014 ohms
Signal output range -10 to +10 volts (maps to ±100 V)
Signal output accuracy ±1%
Batteries four “AA” cells (alkaline recommended)
Battery life approximately 75 hours

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Basic Electrometer ES-9078A
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Technical Support
For assistance with any PASCO product, contact PASCO at:
For the latest revision of this Instruction Manual, visit the PASCO web site and enter ES-9078A in the Search window.
Limited Warranty For a description of the product warranty, see the PASCO catalog. Copyright The PASCO scientific
012-12856A Basic Electrometer Instruction Manual is copyrighted with all rights reserved. Permission is granted to non-profit educa-
tional institutions for reproduction of any part of this manual, providing the reproductions are used only in their laboratories and
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Product End of Life Disposal Instructions:
This electronic product is subject to disposal and recycling regulations that vary by country and region. It is
your responsibility to recycle your electronic equipment per your local environmental laws and regulations to
ensure that it will be recycled in a manner that protects human health and the environment. To find out where
you can drop off your waste equipment for recycling, please contact your local waste recycle/disposal service,
or the place where you purchased the product.
The European Union WEEE (Waste Electronic and Electrical Equipment) symbol and on the product or its
packaging indicates that this product must not be disposed of in a standard waste container.
Address: PASCO scientific
10101 Foothills Blvd.
Roseville, CA 95747-7100
Phone: [phone] (worldwide)
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Fax: [phone]
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